Although advances have been made towards understanding and treating suicidal behavior, suicide rates in this country have not fallen appreciably over the last decade. One explanation for our limited ability to effectively treat suicidality may be our limited understanding of the phenomenology of suicidality as it occurs in the real world. The proposed study, US-TREAT (Understanding Suicide: Translational Research in Emotional Reactivity Assessment Technology), is the first to apply a combination of multimethod in-hospital assessments and ecological momentary assessment (EMA) procedures post-discharge from inpatient care to model a translational phenotype of emotional reactivity, a clinically- and theoretically-important influence on suicidality, and its prediction of future suicdal ideation and behavior. A sample of 300 individuals hospitalized for suicidal ideation and behavior and 50 non-suicidal psychiatric comparisons will participate in a laboratory paradigm to assess physiological response (i.e., heart rate variability, skin conductance, & startle) to standardized environmental stimuli, EMA of emotional reactivity (i.e., affect, affective valence, and rate of change in affect over time), and genetic biomarkers (e.g. serotonin system, neurotrophins). To better characterize and predict the phenomenology of suicidality, we will use analytical models of cyclical processes (i.e., dynamical systems) to permit non-linear modeling of discrete aspects of emotion (i.e., intensity, rate of affect change, cyclicality, and damping) a influenced by experienced (i.e. EMA assessed) life stressors. The US-TREAT approach will provide critical insight regarding the phenomenology of suicidality with clear treatment implications.